Blockade of hippocampal bradykinin B1 receptors improves spatial learning and memory deficits in middle-aged rats

Previous studies have demonstrated that targeting bradykinin receptors is a promising strategy to counteract the cognitive impairment related with aging and Alzheimer's disease (AD). The hippocampus is critical for cognition, and abnormalities in this brain region are linked to the decline in mental ability. Nevertheless, the impact of bradykinin signaling on hippocampal function is unknown. Therefore, we sought to determine the role of hippocampal bradykinin receptors BR and BR on the cognitive decline of middle-aged rats. Twelve-month-old rats exhibited impaired ability to acquire and retrieve spatial information in the Morris water maze task. A single intra-hippocampal injection of the selective BR antagonist des-Arg-[Leu]-bradykinin (DALBK, 3 nmol), but not the selective BR antagonist D-Arg-[Hyp,Thi,D-Tic,Oic]-BK (Hoe 140, 3 nmol), reversed the spatial learning and memory deficits on these animals. However, both drugs did not affect the cognitive function in 3-month-old rats, suggesting absence of nootropic properties. Molecular biology analysis revealed an up-regulation of B1R expression in the hippocampal CA1 sub-region and in the pre-frontal cortex of 12-month-old rats, whereas no changes in the BR expression were observed in middle-aged rats. These findings provide new evidence that inappropriate hippocampal BR expression and activation exert a critical role on the spatial learning and memory deficits in middle-aged rats. Therefore, selective BR antagonists, especially orally active non-peptide antagonists, may represent drugs of potential interest to counteract the age-related cognitive decline

Mechanisms Underlying the Scratching Behavior Induced by the Activation of Proteinase-Activated Receptor-4 in Mice

A role for proteinase-activated receptor-4 (PAR-4) was recently suggested in itch sensation. Here, we investigated the mechanisms underlying the pruriceptive actions of the selective PAR-4 agonist AYPGKF-NH2 (AYP) in mice. Dorsal intradermal (i.d.) administration of AYP elicited intense scratching behavior in mice, which was prevented by the selective PAR-4 antagonist (pepducin P4pal-10). PAR-4 was found to be coexpressed in 32% of tryptase-positive skin mast cells, and AYP caused a 2-fold increase in mast cell degranulation. However, neither the treatment with cromolyn nor the deficiency of mast cells (WBB6F1-KitW/Wv mice) was able to affect AYP-induced itch. PAR-4 was also found on gastrin-releasing peptide (GRP)-positive neurons (pruriceptive fibers), and AYP-induced itch was reduced by the selective GRP receptor antagonist RC-3095. In addition, AYP evoked calcium influx in ∼1.5% of cultured DRG neurons also sensitive to TRPV1 (capsaicin) and/or TRPA1 (AITC) agonists. Importantly, AYP-induced itch was reduced by treatment with either the selective TRPV1 (SB366791), TRPA1 (HC-030031), or NK1 (FK888) receptor antagonists. However, genetic loss of TRPV1, but not of TRPA1, diminished AYP-induced calcium influx in DRG neurons and the scratching behavior in mice. These findings provide evidence that PAR-4 activation by AYP causes pruriceptive itch in mice via a TRPV1/TRPA1-dependent mechanism

An Essential Role for Alzheimer’s-Linked Amyloid Beta Oligomers in Neurodevelopment: Transient Expression of Multiple Proteoforms during Retina Histogenesis

Human amyloid beta peptide (Aβ) is a brain catabolite that at nanomolar concentrations can form neurotoxic oligomers (AβOs), which are known to accumulate in Alzheimer’s disease. Because a predisposition to form neurotoxins seems surprising, we have investigated whether circumstances might exist where AβO accumulation may in fact be beneficial. Our investigation focused on the embryonic chick retina, which expresses the same Aβ as humans. Using conformation-selective antibodies, immunoblots, mass spectrometry, and fluorescence microscopy, we discovered that AβOs are indeed present in the developing retina, where multiple proteoforms are expressed in a highly regulated cell-specific manner. The expression of the AβO proteoforms was selectively associated with transiently expressed phosphorylated Tau (pTau) proteoforms that, like AβOs, are linked to Alzheimer’s disease (AD). To test whether the AβOs were functional in development, embryos were cultured ex ovo and then injected intravitreally with either a beta-site APP-cleaving enzyme 1 (BACE-1) inhibitor or an AβO-selective antibody to prematurely lower the levels of AβOs. The consequence was disrupted histogenesis resulting in dysplasia resembling that seen in various retina pathologies. We suggest the hypothesis that embryonic AβOs are a new type of short-lived peptidergic hormone with a role in neural development. Such a role could help explain why a peptide that manifests deleterious gain-of-function activity when it oligomerizes in the aging brain has been evolutionarily conserved

(A) Outline of the treatments and experimental schedule: memantine (Men, 4 mg/kg), saline (Sal, 0.9%) or pilocarpine (150 mg/kg). (B–C) Effects of memantine on the expression of NMDAR1 (120 kDa) and R2B (180 kDa) in the hippocampus of rats injected with pilocarpine.

<p>Animals were euthanized 24 h or 1 month after treatments. Protein expression levels of NMDARs were determined by Western blot analysis, quantified by densitometric scanning and expressed as a ratio of signal intensity for the target proteins relative to that for β-actin (43 kDa). Each group is represented by illustration of two lanes in order to denote intra-group variations. Data are presented as mean±S.E.M. of 3–6 animals per group. Comparisons were made by two-way ANOVA followed by Student–Newman–Keuls's test. *p≤0.05 or **p≤0.001 as compared with sal+sal group.</p

(A) Outline of the treatments and experimental schedule: saline (Sal, 0.9%) or pilocarpine (Pilo, 150 mg/kg). (B and C) Effects of pilocarpine on plasma levels of CORT (ng/ml) and ACTH (pg/ml) and (D) expression of GRs (85 and 117 kDa) in the hippocampus of rats injected with pilocarpine.

<p>Animals were euthanized 24 h or 1 month after treatments. Protein expression levels of GRs were determined by Western blotting analysis, quantified by densitometric scanning and expressed as a ratio of signal intensity for the target proteins relative to that for β-actin (43 kDa). Data are presented as mean±S.E.M. of 3–6 animals per group. Comparisons were made by Student´s t test. *p≤0.05 or **p<0.001 as compared with saline (control) group.</p